The present invention relates to apparatus for incinerating and melting materials such as organic matters, inorganic matters and metals.
Various apparatus for incinerating and melting materials such as organic matters, inorganic matters and metals (hereinafter referred to as "materials to be treated" or, more simply, as "materials") are known, including such as metal melting furnaces, sewage slurry melting furnaces, apparatus for melting garbage and industrial wastes, and apparatus for burning, melting and solidifying radioactive wastes from nuclear power plants.
These apparatus are generally required to meet the following three requirements:
(1) Easiness of the works for pouring the melt and for stopping the pouring, and free adjustment of the period of stay of materials to be treated in the furnace. These are necessary for easy and safe pouring and stopping of pouring of holt melt, and also for free start and stop of the pouring of melt regardless of the amount of the melt in the furnace, so as to allow optimization of the heating and mixing time, i.e., the period of stay of the melt, in accordance with the nature of materials to be treated.
(2) Smooth discharge of the melt from the furnace without fail. Any blockage of the melt discharge port by locally solidified or unmolten materials has to be avoided strictly.
(3) A series of disposing processes including the burning, melting, pouring and cooling has to be completed in an airtight atmosphere. This is necessary in order to prevent scattering of fume and dust freed from the materials to be treated when they are molten, and also for preventing transfer of any noxious substances freed from the material when there is a risk of release of such substances.
Although several types of incinerating and melting apparatus have been used, these known apparatus have disadvantages as follows:
A. Apparatus of the type which has a discharge port in the bottom thereof and in which the start and stop of the melt is controlled by means of a slide gate adapted to open and close the discharge port.
This type of apparatus tends to suffer from blockage of the discharge portion, and requires a frequent protective maintenance due to rapid wear of the slide gate and associated parts.
B. Apparatus of the type in which the melt discharge port is provided in one side or bottom thereof, the closing of the port being effected by solidifying the melt by forcible cooling of the region near the discharge port, the start of discharge being effected by locally heating the region around the discharge port so as to melt the solidified materials.
This apparatus requires a huge equipment and complicated operation for the start and stop of pouring.
C. Apparatus of the type in which the melt is discharged by overflow through an overflow port formed in one side thereof.
This type of apparatus tends to experience blockage of the overflow port, and requires a careful control of the material supply rate, as well as the nature of the melt, in order to effectively control the period of stay of the materials in the furnace.
D. Apparatus of the type in which the materials to be treated are heated, melted and solidified in a vessel or a mold. In this case, measures have to be taken for the heat resistance and heat insulation of the vessel which is heated both by a heating source and the melt, and is not suitable for use in continuous or semi-continuous operation.
E. Apparatus of the type in which the surface area of the materials to be treated is molten and the melt is continuously discharged from the bottom of the heating chamber by the force of gravity. Apparatus of this type encounters a problem such that, since there is no pool of the melt, the period of stay of the materials to be treated tends to become short, resulting in insufficient melting and mixing.
F. Apparatus of the type in which the materials to be treated are heated and molten in an open heating chamber and, after the melting, the chamber is tilted to discharge the melt.
This apparatus permits a free adjustment of the staying period of the melt and can make sure the discharge of the melt. However, apparatus of this type encounters a difficulty in conducting the pouring under an airtight condition, and is not suitable for use in continuous or semi-continuous treatment.
Thus, all the known incinerating and melting apparatus involve their own problems.
On the other hand, the incinerating, melting and solidifying treatment of radioactive wastes requires that the melt can be safely taken out of the furnace without fail and that the series of treatment be conducted under an airtight condition, and there is a demand for development of apparatus which can satisfy such requirements.